J. Nannoplankton Res., 39(1), 2021, pp. 3–13 © 2021 International Nannoplankton Association
ISSN 1210-8049 Printed by The Sheridan Press, USA

3

Two new species of Hornibrookina Edwards, 1973 from theAustral Basin, Patagonia: Biostratigraphical andpalaeoecological implications
Juan P. Pérez Panera*
CONICET–YPF Tecnología, Av. del Petróleo s/n, 1923 Berisso, Buenos Aires, Argentina; perezpanera@gmail.com

Diana I. Ronchi
GEMA SRL – YPF Tecnología, Av. del Petróleo s/n, 1923 Berisso, Buenos Aires, Argentina; sianaronchi@gmail.com
Manuscript received 1st May, 2020; revised manuscript accepted 9th February, 2021

Abstract Two new species of the genus Hornibrookina––H. larae sp. nov. and H. nicolasii sp. nov.––are described and illustrated. These species were first reported from surface and subsurface Early to Middle Eocene sedimentary successions in the Austral Basin, Patagonia, Argentina. Accompanying calcareous nannofossils and foraminifera from an outcrop sample from the Río de la Turba area, where these new species are well preserved andabundant, are discussed to better constrain the age and palaeoecology of the new species. These new species extend
the geological range of the genus Hornibrookina into the Late Lutetian–Early Bartonian (NP16) and support its affinity for coastal, eutrophic marine conditions.

Keywords Hornibrookina larae, Hornibrookina nicolasii, Middle Eocene, biostratigraphy, palaeoecology, South
Atlantic Ocean

1. Introduction
Biostratigraphical investigations conducted byoil industry personnel in the Austral Basin, Patagonia, Argentina revealed the presence of two
new species of Hornibrookina Edwards, 1973.
These species had been previously documented
from cuttings of Early to Middle Eocene subsurface successions from different parts of theAustral Basin. Recently, they were both recorded in a moderately to well-preserved assemblage of calcareous nannofossils from a Middle
Eocene outcrop in the Isla Grande de Tierradel Fuego, Argentina (Figure 1). In this material, the stratigraphical uncertainties associatedwith cuttings were avoided, and planktonic andbenthic foraminifera were able to provide additional age constraints for these new species.
The purpose of this contribution is to describe
and illustrate these new species and to highlightwhat this discovery means regarding the evolution and palaeoecology of the genus Hornibrookina.
2. Geological background
The Austral Basin lies in southern SouthAmerica and spans part of Patagonia and theKey
Basin border
Tectonic limit
Basin basement
Well
Outcrop

Figure 1: Map of southern Patagonia showing the extent of the Austral Basin (dotted area) and the locations of the mentioned sites. Modified after Nullo et al. (1999).
CB––Campo Bola Well, CO––Cóndor Oeste Well, Ca––Carpintero Well, RdlT––Ríode la Turba outcrop

4

Pérez Panera, Ronchi

Argentinian Continental Shelf, including the Isla Grandede Tierra del Fuego (Figure 1). It developed between the
Andean Cordillera to the west and the Rio Chico High on
the Patagonian Shelf to the east (Malumián, 1999; Nullo
et al., 1999). Together with the adjacent, offshore Malvinas Basin, it formed near a complex tectonic area, which
was greatly affected by interaction between the SouthAmerican, Scotia and Antarctic Plates (Galeazzi, 1998).
Sedimentary infilling of the basin started in the Late Jurassic, and was triggered by the extensional tectonics thatfragmented Gondwana and caused the early opening of theSouth Atlantic Ocean (Peroni et al., 2002). The Late Jurassic to Miocene sediments in this basin are predominantly
marine and have a maximum thickness of up to 7000 m(Galeazzi, 1998). During the Late Cretaceous, the Austral
Basin transformed into a foreland basin that accumulated
the mainly fine-grained sediments of the Inoceramus beds
(Olivero & Malumián, 2008; Sachse et al., 2015). From
the Maastrichtian, the basin was subjected to changing
sea levels, with the main Atlantic transgressions occurring
during the Maastrichtian–Danian, the Middle Eocene, theLate Oligocene–Early Miocene and the Middle Miocene(Malumián & Náñez, 2011; Pérez Panera, 2013). The Palaeogene sedimentary cycles have distinctly different facies in different parts of the basin (Malumián, 1999, 2002;
Olivero & Malumián, 2008). During this time, the deepest
areas were in the south-eastern sector, near the Isla Grandede Tierra del Fuego and the Argentinian Continental Shelf.
Sediments in the central and western parts of the basin
were deposited in shallow-marine to continental environments.
3. Materials and methods
Cuttings samples from three industry wells (Carpintero,
Chile, Cóndor Oeste and Campo Bola, Argentina) and one
outcrop sample, (022) from the Río de la Turba outcrop
preserving the La Despedida Group, were prepared fornannofossil analysis using the gravity settling techniqueof Bramlette & Sullivan (1961). The slides were scanned
at 1000x magnification under polarised light using a Leica
DM 2700P microscope, whilst a Leica DFC 295 digital
camera was used to take photographs. Samples for scanning electron microscope (SEM) analysis were preparedfrom the Río de la Turba outcrop using a vacuum pumpfor filtration onto a 0.45-µm-pore, 47-mm-diameter Millipore filter, with the addition of a few drops of a commer-

cial glass-cleaning product to disperse the clays. An FEI
Quanta 200 SEM was used to take photographs.
For the foraminiferal analysis, 20 g of washed rock
was placed into a beaker to which 500 ml of water and
50 ml of 100-volume hydrogen peroxide were added.
The sample was then boiled for 30 min to facilitate disaggregation. The material was washed under running water
through a 74-µm-mesh sieve (200 Tyler Screen System)and dried in a sand bath. Five grammes of sediment wereextracted from the residue for analysis. The foraminifera
were picked and arranged onto slides for identification.
The samples are stored in the YPF Tecnología SA Micropaleontological Repository (with the prefix YT.RMP_#)and the Facultad de Ciencias Exactas y Naturales of the
Universidad Nacional de Buenos Aires micropalaeontological collection (with the prefix BAFC–NP).
4. Micropalaeontological results from the
Río de la Turba outcrop
A moderately to well-preserved calcareous nannofossil assemblage was recovered from Sample 022 (Table 1), in
which a total of 23 taxa were identified. The most abundant species––Reticulofenestra minuta––had a relative
abundance of >50%, while the second most abundant species––Hornibrookina larae sp. nov.––represented 17.5%.
The other relevant taxa were Hornibrookina nicolasii sp.
nov., Reticulofenestra daviesii, R. lockeri, R. reticulata,
small specimens of R. bisecta, R. dictyoda, Cyclicargolithus ﬂoridanus, Toweius callosus, T. rotundus, Pontosphaera pygmaea, P. pulchra, Clausicoccus fenestratus,
C. subdistichus and Sphenolithus predistentus, among
others (Table 1).
The benthic and planktonic foraminifera were moderately preserved, with the species richness and diversity being high among the benthics (Table 2). The most abundant
benthic taxa were Martinotiella communis, Spiroplectammina elgansoensis, S. spectabilis (agglutinated forms)
and Anomalinoides pinguiglabra, Bulimina sp., Cibicides
wuellerstorfi, other unidentified Cibicides spp., Cribrorotalia spp., Globocassidulina subglobosa, Gyroidinoides
ex gr. zelandica, Heterolepa perlucida, Lenticulina alatolimbata, Uvigerina peregrina and Virgulinella severini(calcareous forms). The planktonic foraminifera weremoderately abundant, but most could not be identified to
species level due to poor preservation. The only recognisable species were Globigerinatheka index, Catapsydrax

New species of Hornibrookina from Patagonia

5

Table 1: Nannofossils recovered from Sample 022, Río de la Turba, La Despedida Group, Austral Basin, Isla Grande de Tierra del Fuego, Argentina

Table 2: Foraminifera recovered from Sample 022, Río de la Turba, La Despedida Group, Austral Basin, Isla Grande de Tierra del Fuego, Argentina.
P––porcellaneousunicavus and Subbotina angiporoides (Table 2). The ageof the Río de la Turba outcrop is Middle Eocene, based on
a combination of calcareous nannofossil and foraminifera
biostratigraphy.
5. Systematic palaeontology
Order ISOCHRYSIDALES Pascher, 1910
Family PRINSIACEAE Hay & Mohler, 1967 emend.
Young & Bown, 1997
Genus Hornibrookina Edwards, 1973
Type species Hornibrookina teuriensis Edwards, 1973
Diagnosis: Narrowly elliptical placoliths with a centralarea filled by large bars. The proximal shield is monocyclic. The distal shield is bicyclic, with the inner cycle
forming a crown-like structure (Young & Bown, 1997).
Hornibrookina larae Pérez Panera sp. nov.
Pl. 1, figs 1–9; Pl. 2, figs 1–16
2013 Hornibrookina weimerae Self-Trail, 2011: Pérez
Panera, pp. 129–130.
Derivation of name: Named in honour of Lara Pérez
Panera, daughter of Juan P. Pérez Panera. Diagnosis: Small

Hornibrookina with eight to nine parallel pairs of laths in
the central-area and one cycle of elements in the proximal
shield. Description: Small, elliptical placolith with a medium to large central-area occupied by eight to nine pairsof laths that are aligned perpendicular to the major axis of
the ellipse. Each pair of laths meets at the centre and theirends may be enlarged. There is no longitudinal bar. The
distal shield is composed of two cycles of elements. In the
inner cycle, the elements are high and slightly imbricatedclockwise in distal view. The outer cycle is thin, flat andhas low birefringence in cross-polarised light. The proximal shield is composed of only one cycle of elements, towhich the eight or nine pairs of laths are attached. The elements of the distal and proximal shields become detachedfrom each other as they approach the rim of the placolith,
producing a spinose or serrated outline, but this could be
due to dissolution. Under crossed polarisers, the tube ishighly birefringent and the outline of the coccolith appears
weakly serrated; the central-area is always dark. Differentiation: Hornibrookina larae differs from H. weimerae inbeing slightly larger and wider, and by having thin laths,
rather than flat, overlapping laths, in the central-area. This
species is difficult to distinguish with the light-microscope(LM), but the central-area in H. larae is dark and the coccolith outline is slightly serrated, whereas, in H. weimerae,

6

Pérez Panera, Ronchi

the central-area is poorly birefringent and the coccolith
outline is smooth. Hornibrookina larae differs from H.
nicolasii in its smaller size, relatively thinner distal shield,
monocyclic proximal shield, and the different number andarrangement of the laths. Remarks: Most of the SEM illustrations of the specimens in Plate 1 show strong dissolution and are poorly preserved. Dissolution most likely
occurred during preparation of the SEM sample. The addition of the glass-cleaner product to the sample worked
perfectly in eliminating the clay, but may have affected thedelicate, small nannofossils, such as H. larae. However,these specimens are still useful for determining the number and arrangement of the laths in the central-area andthe nature of the distal and proximal shields. Dimensions:
Length = 2.33–3.50 µm; width = 1.40–2.50 µm; axial ratio= 1.36–2.00 (Table 3). Holotype: YT.RMP_N.000007.2-1(Pl. 1, fig. 1). Paratypes: YT.RMP_N.000007.2-2
(Pl.
1,
fig.
2), YT.RMP_N.000007.2-3
(Pl.
1,
fig.
3),
YT.RMP_N.000007.2-4
(Pl.
1,
fig.
4), YT.RMP_N.000007.2-5
(Pl.
1,
fig.
5),
YT.RMP_N.000007.2-6
(Pl.
1,
fig.
6),
YT.RMP_N.000007.2-7
(Pl.
1,
fig.
7),
YT.RMP_N.000007.2-8
(Pl.
1,
fig.
8),
YT.RMP_N.000007.2-9
(Pl.
1,
fig.
9),
YT.RMP_N.000007.1-1
(Pl.
2,
fig.
1),
YT.RMP_N.000007.1-2 (Pl. 2, figs 2–5), BAFC-NP
3397-1 (Pl. 2, fig. 6), BAFC-NP 3397-2 (Pl. 2, fig. 7),
BAFC-NP 3397-3 (Pl. 2, fig. 8), YT.RMP_N.000009.1-1(Pl. 2, fig. 9), YT.RMP_N.000009.1-2 (Pl. 2, figs
10–12), YT.RMP_N.000009.1-3 (Pl. 2, fig. 13),YT.RMP_N.000009.1-4 (Pl. 2, fig. 14), BAFC-NP 33974 (Pl. 2, fig. 15), BAFC-NP 3397-5 (Pl. 2, fig. 16). Type
locality: Río de la Turba section, Argentina (53.92˚S,
68.38˚W). Type level: Sample 022, La Despedida Group,
NP16, Middle Eocene. Occurrence: Early to Middle Eocene (NP13–NP16) in the Austral Basin, Patagonia. Ypresian in the Carpintero Well (1300–1310 m depth); Late
Ypresian to Early Bartonian (NP13–NP16) in the Campo
Bola Well (1025–1030 to 1015–1020 m); Lutetian to Early
Bartonian (NP15–NP16) in the Cóndor Oeste Well (1065–
1105 m); Late Lutetian to Early Bartonian (NP16) in the
Río de la Turba outcrop.

Hornibrookina nicolasii Pérez Panera sp. nov.
Pl. 3, figs 1–9; Pl. 4, figs 1–30
Derivation of name: Named in honour of Nicolás Pérez
Panera, son of Juan P. Pérez Panera. Diagnosis: A medium-sized species of Hornibrookina with a broad, bicyclic distal shield, broad, monocyclic proximal shield andcentral-area filled by 11 to 14 pairs of alternating laths.
Description: Medium-sized, elliptical placolith with abroad, bicyclic distal shield and a medium to large centralarea occupied by 11 to 14 flattened pairs of laths that areperpendicular to the inner wall of the shield. The junctionof the laths is slightly offset and forms parallel to the major axis of the ellipse. Overgrowth can result in enlarged
ends on the laths, which form a ‘hammer’ shape. There isno separate longitudinal bar. The outer cycle of the distal
shield is broad and the elements are slightly imbricatedclockwise in distal view. The elements have a trapezoidal
shape and are thinner towards the central-area. This produces a conspicuous slit between the elements that is also
distinctive in the LM. The inner cycle of the distal shield
is tall and thin. In some specimens, protruding knobs havedeveloped at the contact between the outer and inner cycles of the distal shield. The proximal shield is also broad,but smaller than the distal shield. Under crossed polars,
the inner cycle of the distal shield is highly birefringent,
while the outer cycle has low birefringence and a serrated
aspect due to the thinning of the elements between the sutures. The central-area has low birefringence and, in somecases, a bright line appears subparallel to the major axisof the ellipse. This is due to the enlargement of the laths
where they connect and not because of the presence of alongitudinal bar. Differentiation: Hornibrookina nicolasii
differs from other species of the genus in having an outercycle of elements with slits between them, which givesa spinose aspect under crossed polarisers. It also differsfrom the co-occurring H. larae in its larger size and different arrangement of laths. Remarks: When observed undercrossed polarisers and with a gypsum plate, the tube anddistal shield elements show the same crystallographic orientation (Pl. 4, figs 10, 14). This is not the case in otherspecies of Hornibrookina, where the tube elements correspond to R-units and the shield elements to V-units, producing an alternation of colours between the tube and the
distal shield. However, it is possible that the birefringent
elements correspond to the proximal shield elements that

New species of Hornibrookina from Patagonia

7

Table 3: Hornibrookina larae and H. nicolasii measurements from SEM specimens

are R-units and not to the distal shield elements. In any
case, this new species is included in the genus Hornibrookina because it presents the diagnostic characteristics ofthe genus, in being a narrowly elliptical placolith with acentral-area filled by large bars, having a monocyclic proximal shield, and with a bicyclic distal shield with an innercycle forming a crown-like structure. Dimensions: Length= 5.48–6.15 µm; width = 3.66–4.46 µm; axial ratio =1.34–1.56 (Table 3). Holotype: YT.RMP_N.000007.2-10(Pl. 3, figs 1, 2). Paratypes: YT.RMP_N.000007.2-11
(Pl.
3,
fig.
3),
YT.RMP_N.000007-12
(Pl.
3,
fig.
4),
YT.RMP_N.000007.2-13(Pl.
3,
fig. 5), YT.RMP_N.000007.2-14 (Pl. 3, fig.
6), YT.RMP_N.000007.2-15 (Pl. 3, fig. 7),
YT.RMP_N.000007.2-16
(Pl.
3,
fig.
8),
YT.RMP_N.000007.2-17
(Pl.
3,
fig.
9),
YT.RMP_N.000007.1-3
(Pl.
4,
figs
1–5),
YT.RMP_N.000007.1-4
(Pl.
4,
figs
6–15),
YT.RMP_N.000007.1-5
(Pl.
4,
fig.
16),
YT.RMP_N.000007.1-6
(Pl.
4,
fig.
17),
YT.RMP_N.000007.1-7
(Pl.
4,
fig.
18),

YT.RMP_N.000007.1-8 (Pl. 4, figs 19, 20),
YT.RMP_N.000007.1-9 (Pl. 4, figs 21–24), BAFC-NP
3397-6 (Pl. 4, fig. 25), BAFC-NP 3397-7 (Pl. 4, fig. 26),
BAFC-NP 3397-8 (Pl. 4, fig. 27), BAFC-NP 3397-9 (Pl.
4, fig. 28), BAFC-NP 3397-10 (Pl. 4, fig. 29), BAFC-NP
3397-11 (Pl. 4, fig. 30). Type locality: Río de la Turba
section, Argentina (53.92˚S, 68.38˚W). Type level: Sample 022, La Despedida Group, NP16, Middle Eocene. Occurrence: Early to Middle Eocene (NP13–NP16) in theAustral Basin, Patagonia. Late Ypresian to Early Bartonian (NP13–NP16) in the Campo Bola Well (1015–1020m); Late Lutetian to Early Bartonian (NP16) in the Río dela Turba outcrop.
6. Age and palaeoenvironment:
Implications for Hornibrookina evolution
and palaeoecology
Previous foraminiferal analyses of the Río de la Turba
outcrop have indicated a Middle Eocene age for this unit
(Malumián, 1989, 1990). In terms of nannofossils, basedon the co-occurrence of Sphenolithus predistentus and8

Pérez Panera, Ronchi

Plate 1
SEM images of Hornibrookina larae, Río de la Turba, Sample 022
1: holotype; 2–9: paratypes; 3, 7, 9: proximal views

YT.RMP_N.000007.2-1

YT.RMP_N.000007.2-4

YT.RMP_N.000007.2-7

YT.RMP_N.000007.2-2

YT.RMP_N.000007.2-5

YT.RMP_N.000007.2-8

Reticulofenestra reticulata, which have their base occurrences at or near the base of NP16 of Martini (1971) (seeBown & Dunkley Jones, 2012; Agnini et al., 2014; Raffi etal., 2016), with Toweius callosus, which has a top near the
NP15/NP16 boundary, we constrained the age of the Ríode la Turba outcrop to the Middle Eocene (NP16). The newforaminifera data is in agreement with a Middle Eocene
age; the planktonic foraminifera species Globigerinatheka
index is restricted to the Middle to Late Eocene (Premoli
Silva et al. 2006), and its base lies at the E9/E10 biozone
boundary of Berggren & Pearson (2005), which coincides

YT.RMP_N.000007.2-3

YT.RMP_N.000007.2-6

YT.RMP_N.000007.2-9

with the base of NP16. The benthic foraminiferal assemblage also supports this age and can be correlated to otherknown Middle Eocene assemblages in the Austral Basin(Malumián & Jannou, 2010; Malumián & Náñez, 2011).
A comparison of the assemblage from the Río de laTurba section with other Middle Eocene nannofossil assemblages from the Austral Basin revealed some differences in the taxonomic composition and relative abundances (see Pérez Panera, 2009, 2013). The most evident
was the absence of the genus Chiasmolithus, which iscommon and diverse in other Middle Eocene assemblag-

New species of Hornibrookina from Patagonia

9

Plate 2
LM paratype images of Hornibrookina larae
1–5: Río de la Turba, Sample 022;
6–8, 15, 16: Campo Bola, 1015–1020 m; 9–14: Cóndor Oeste, 1065 m

YT.RMP_N.000007.1-1

YT.RMP_N.000007.1-2

BAFC-NP 3397-1

YT.RMP_N.000009.1-1

YT.RMP_N.000009.1-2

YT.RMP_N.000009.1-3

YT.RMP_N.000009.1-4

es, the high relative abundance of Reticulofenestra minuta,
the small size of other reticulofenestrids (see Table 1) andthe higher relative abundances of H. larae and H. nicolasii. The abundance of Hornibrookina in the Río de laTurba section is unusually high and most likely related
to the palaeoenvironmental conditions. High abundances

BAFC-NP 3397-2

BAFC-NP 3397-3

BAFC-NP 3397-4

BAFC-NP 3397-5

of small reticulofenestrids and, more specifically, of R.
minuta, have been associated with high productivity (Pujos, 1985; Gartner, 1992). Moreover, according to Wade
& Bown (2006) and Auer et al. (2014), R. minuta blooms
may have been triggered by enhanced terrigenous nutrient input, generating eutrophic conditions and fluctuating

10

Pérez Panera, Ronchi

Plate 3
SEM images of Hornibrookina nicolasii, Río de la Turba, Sample 022
1, 2: holotype; 3–9: paratypes; 8, 9: proximal views

HOLOTYPE
YT.RMP_N.000007.2-10

YT.RMP_N.000007.2-12

YT.RMP_N.000007.2-15

YT.RMP_N.000007.2-11

YT.RMP_N.000007.2-13

YT.RMP_N.000007.2-16

salinity. Schneider et al. (2013) and Leon y Leon et al.
(2018) have suggested that the genus Hornibrookina had
an affinity for coastal, eutrophic surface waters, and therelatively high abundance of these new species in this assemblage supports that palaeoecological interpretation.
The moderately abundant planktonic and diverse benthic foraminifera might indicate middle- to outer-shelf

YT.RMP_N.000007.2-14

YT.RMP_N.000007.2-17

depths with high-productivity surface waters. Also, apalynological analysis of this sample documented a highabundance of pollen and spores and scarce, poorly preserved dinoflagellate cysts (Pérez Panera et al., 2018). In
summary, according to the nannofossil and foraminifera
assemblage characteristics, supported by the presence ofabundant continental palynomorphs, these sediments wereNew species of Hornibrookina from Patagonia

11

Plate 4
LM paratype images of Hornibrookina nicolasii
1–24: Río de la Turba, Sample 022; 25–30: Campo Bola, 1015–1020 m

YT.RMP_N.000007.1-3

YT.RMP_N.000007.1-4

YT.RMP_N.000007.1-4

YT.RMP_N.000007.1-5

YT.RMP_N.000007.1-6

YT.RMP_N.000007.1-7

YT.RMP_N.000007.1-8

YT.RMP_N.000007.1-9

BAFC-NP 3397-7

BAFC-NP 3397-6

BAFC-NP 3397-8

BAFC-NP 3397-9

BAFC-NP 3397-10

BAFC-NP 3397-11

12

Pérez Panera, Ronchi

deposited in ~100–200-m water depths, but relatively
close to the coast, and with eutrophic surface waters probably resulting from a high influx of nutrients from continental runoff.
The youngest known occurrence of the genus Hornibrookina has been documented by Self-Trail (2011), whorecorded H. arca just above the base of NP11 (Early Eocene) on the North American shelf. However, Pérez Panera (2013) recorded specimens of what he initially called H.
weimerae from Early to Middle Eocene cuttings from theAustral Basin. These latter specimens are now considered
to be the new species H. larae, and a re-examination of the
Carpintero, Cóndor Oeste and Campo Bola well samples
has revealed the presence of both H. larae and H. nicolasii
from NP13 to NP16. However, a gap in the occurrence ofthe genus still persists in the Early Eocene of upper NP11
and NP12. The diversity and abundance of this genus diminished across the Paleocene–Eocene transition and during the extreme climate changes of the Early Eocene hyperthermal events, but managed to survive in relict areas,such as the Austral Basin.

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Micropaleontology, 111: 53–65.
Berggren, W.A. & Pearson, P.N. 2005. A revised tropical to subtropical Paleogene planktonic foraminiferal zonation. Journal of Foraminiferal Research, 35: 279–298.
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from the Paleogene equatorial Pacific (IODP Expedition 320
Sites U1331–1334). Journal of Nannoplankton Research,
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Bramlette, M.N. & Sullivan, F.R. 1961. Coccolithophorids andrelated nannoplankton of the early Tertiary in California. Micropaleontology, 2: 129–188.
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7. Conclusions
The two new species––Hornibrookina larae and H. nicolasii––range from the Early (NP13) to Middle (NP16)
Eocene of the Austral Basin, extending the known stratigraphic record of the genus. However, to date, there is no
known record of the genus in the NP11–NP12 interval.
According to the characteristics of the nannofossil andforaminiferal assemblages in which these new species occurred most abundantly, the coastal and eutrophic affinityof the genus is reinforced.

Galeazzi, J.S. 1998. Structural and stratigraphic evolution of theWestern Malvinas Basin. Bulletin of the American Association of Petroleum Geologists, 82: 596–636.
Gartner, S. 1992. Miocene nannofossil chronology in the North
Atlantic, DSDP Site 608. Marine Micropaleontology, 18:
307–331.
Hay, W.W. & Mohler, H.P. 1967. Calcareous nannoplankton
from Early Tertiary rocks at Pont Labau, France and Paleocene–Early Eocene correlations. Journal of Paleontology,
41: 1505–1541.
Leon y Leon, I.A., Bralower, T.B. & Self-Trail, J.M. 2018. Eco-

Acknowledgements

logical changes in the nannoplankton community across

We want to thank YPF S.A. (Argentina) and YPF Tecnología

a shelf transect during the onset of the Paleocene–Eocene

S.A. (Argentina) for permission to publish this work. Thanks

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